Plenty of homeowners have figured out a quick way to make a buck—rent out a room or your entire apartment to out-of-towners—whether they’re short-term travelers or in town for an event. Now here’s the catch. What you’re doing may not be legal.

Last month, a New York judge ruled that a man who used AirBnB broke the law. His crime? Renting out his apartment for less than 30 days. The law is really meant to protect against landlords running illegal sublets.

But remember, to operate a traditional hotel or B&B, it requires official licensing and…paying taxes. Services like AirBnB and VRBO don’t necessarily follow these rules.

It’s not just New York you have to worry about. San Francisco has a similar law on the books that prevents short-term rentals in buildings with four or more units.

So, it’s up to you to know the laws. Before you list your home on a vacation rental city, look into your local city and state legislation. And if you’re renting, be sure to read the fine print on your lease.

Keep reading for more travel tips.